The present invention relates to deflectable elements which are suitable for use, with appropriate electronics, as either force transducers or actuators.
It is known to fabricate force transducers from silicon substrates by etching suspended beams, or similar structures, which deflect in response to the application of a force to be measured. The deflection may be electronically measured by conventional means such as resistive strain gauges or piezoelectric elements. Typical applications of these force transducers include accelerometers, pressure sensors, gravity sensors, and microphones.
A difficulty encountered with many known devices is that internal bending moments of the suspended structure are cancelled by reactions at the fixed boundary which prohibit flexure with simultaneous boundary displacement. Stated another way, these devices typically have not provided rectilinear displacement of the suspended structure. Accordingly, a nonlinearity has been introduced into the electrical representation of the applied force. Another problem is that the amount of flexure is limited by the amount of bending a given dimension of a silicon structure is able to withstand before fracturing.
A prior approach to provide rectilinear displacement of a suspended element is disclosed in U.S. Pat. No. 4,071,838. More specifically, a structure is disclosed which may be characterized as a pair of opposing E-shaped springs joined together at their, arm extremities and fabricated from a single monocrystalline wafer. The resulting center arm allegedly deflects in a rectilinear relationship to the applied force. A disadvantage of this approach is the complexity of the structure and associated complexity in fabricating. Another disadvantage is that the range of rectilinear displacement is limited by the amount of bending the silicon segments are able to withstand before fracturing.
In another approach, U.S. Pat. No. 4,144,516 discloses a multiple wafer structure, each wafer having a pair of opposing E-shaped springs. The two wafers are bonded together to extend the range of rectilinear deflection of the E-shaped springs. A disadvantage of this approach is the added complex:ty of the two wafer design.